Alignment of a patterned electron beam with a member by electron backscatter

ABSTRACT

A patterned electron beam from a photocathode source is aligned with precisely located areas of a major surface of a member. At least one and preferably two detector marks of predetermined shape are located, preferably widely spaced away, adjacent the major surface of the member, and corresponding detector means are positioned adjacent periphery portions of the member. Each detector mark is capable of producing backscattered electrons on irradiation by an electron beam, and each detector means is capable of detecting backscattered electrons from the corresponding detector mark and producing an electrical signal corresponding to the area of the corresponding mark irradiated by an electron beam. The patterned electron beam to be aligned has at least one alignment beam portion of predetermined crosssectional shape and corresponds to a detector mark. The backscattered electrons produced by impingement of the alignment beam portions on the corresponding detector marks are detected by the detector means. The position of the electron beam is moved relative to the member until the backscattering detected by the detector means indicates alignment of the alignment beam portions with the corresponding detector marks.

ll-l9-7 Nov. 19, 1974 ALIGNMENT OF A PATTERNED ELECTRON BEAM WITH AMEMBER BY ELECTRON BACKSCATTER OKeeffe et a1. 250/492 A Ferty 2501492 APrimary Examiner-James W. Lawrence Assistant Examiner-C. E. ChurchAttorney, Agent, or FirmC. L. Menzemer [5 7] ABSTRACT A patternedelectron beam from a photocathode source is aligned with preciselylocated areas of a major surface of a member. At least one andpreferably two detector marks of predetermined shape are located,preferably widely spaced away, adjacent the major surface of the member,and corresponding detector means are positioned adjacent peripheryportions of the member. Each detector mark is capable of producingbackscattered electrons on irradiation by an electron beam, and eachdetector means is capable of detecting backscattered electrons from thecorresponding detector mark and producing an electrical signalcorresponding to the area of the corresponding mark irradiated by anelectron beam. The patterned electron beam to be aligned has at leastone alignment beam portion of predetermined cross-sectional shape andcorresponds to a detector mark. The backseattered electrons produced byimpingement of the alignment beam portions on the corresponding detectormarks are detected by the detector means. The position of the electronbeam is moved relative to the member until the backscattering detectedby the detector means indicates alignment of the alignment beam portionswith the corresponding detector marks.

13 Claims, 6 Drawing Figures PATENTE HUV I 91974 SHEET 1 0F 3 Y- ERRORMAGNIFICATION ERROR PATENTEL, rm 1 91914 3'. 849.659

- SHEH 2 0F 3 SCATTERING a RANGE 502.5kev

?5- lOkev I I i I 4.2----- I I RANGE m 1 I MILLIMETERS I i I I E O l l ll l l l I I l 0 IO 20 3O 4O 5O 6O 7O 8O 90 I00 TRAJECTOR-Y ANGLE OFBACKSCATTER IN DEGREES ALIGNMENT OF A PA'ITERNED ELECTRON BEAM WITH AMEMBER BY ELECTRON BACKSCATTER GOVERNMENT CONTRACT This invention ismade in the course of or under Government Contract F 336l5-67-C-1335.

FIELD OF THE INVENTION The invention relates to the making of integratedcircuits and other micro-miniature electronic components with submicronaccuracy.

BACKGROUND OF THE INVENTION The present invention is an improvement onthe electron beam fabrication system described in U.S. Pat. No.3,679,497, granted July 25, 1972, and the alignment system therefordescribed in U.S. Pat. No. 3,710,101, granted Jan. 9, 1973, both ofwhich are assigned to the same assignee as the assignee of the presentapplication.

In said fabrication system, a planar photocathode source (called anelectromask) produces a patterned beam of electron radiation which isdirected onto an electron sensitive layer (called an electroresist) on amajor surface of a member spaced from the photocathode. The patternedbeam causes a precisely patterned differential in solubility betweenirradiated and unirradiated areas of the sensitive layer correspondingto the patterned electron beam. The pattern in differential solubilityis transferred to a pattern in a component layer or body by removing theless soluble portion of the electroresist layer (i.e. either theirradiated or unirradiated portion) to form a window pattern therein,and subsequently selectively etching and doping the component layer orbody through the window pattern developed in the resist layer, ordepositing a component layer by evaporation, sputtering, oxidizing orepitaxially growing through the window pattern in the electroresistlayer.

The resolution of the electron image projection system, e.g. less than0.5 micron, is, however, lost in the juxtaposition of component patternsunless the same resolution can be maintained in the alignment ofsuccessive electromasks with the same member. Making of an integratedcircuit device requires, for example, registration and irradiation of atleast 2 to different component patterns in electroresist layers that aresubsequently developed and transferred to a component layer by etching,doping or deposition. The electron radiation for each pattern must bealigned with precisely located areas of the major surface each time witha precision of 0.5 micron or less with respect to the first pattern.Otherwise, the precision and economies of the electron image projectionsystem will not beobtained in the finished integrated circuit device.

Apparatus has been developed for precision juxtapositioning of multiplecomponent patterns by electron beam induced conductivity marks (EBIC).See U.S. Pat. No. 3,710,101 issued Jan. 9, 1973 and U.S. Pat.application Ser. No. 264,699, filed June 20, 1972, and assigned to thesame assignee asthe present application. A small indexing electron beampattern or mark of predetermined shape is provided on the photocathodesource to produce an alignment beam portion, and a detector mark ofpredetermined shape is formed on an oxide layer on the member andoverlaid with a metal layer. A DC potential is applied across the oxidelayer between the metal layer and the member. The current flow betweenthe potential and the terminals will vary in proportion to the portionor area of the detector mark irradiated by the alignment beam portion.Thus, the alignment beam portion can be precisely aligned with thedetector mark by reading the electron induced current corresponding tothe area of the detector mark irradiated. The electrical current flowmay be processed through an amplifier to actuate a servomechanism tomove the photocathode source or the member, or change the magnetic fieldformed by focusing and deflecting electromagnets surrounding thephotocathode source and member to align and direct the electron beampattern, and in turn provide automatic alignment of the alignment beamportion and the detector mark.

One of the difficulties with this alignment system is that it requiresfabrication of the detector mark on the member itself. Moreover, itusually requires one or more extra fabrication steps to form thedetector marks. The present invention overcomes these difficulties anddisadvantages and provides an alternative method and apparatus forprecision alignment of an electron beam with selected areas of a majorsurface of a member. Specifically, the present invention provides analignment system which can be utilized with negligible interference withthe usual fabrication sequence.

Backscattering detection has been previously used to align a scanningelectron microscope. In the electron microscope, a single beam of finedimension, e.g. 0.2 micron in diameter, is projected onto the surface ofa member and selectively irradiates portions of the surface by movingthrough a matrix on command from a computer. The detector means fordetection of the backscattered electrons were placed opposite each otheradjacent the electron beam source. Such an alignment system is, however,not operative in the electron image projection system because of theelectric and magnetic fields present. Indeed, it would logically beconsidered impossible to adapt the backscattering technique to align theelectron image projection system because of the need for high intensityelectric and magnetic fields in the space between the photocathodesource and the selectively irradiated member.

However, it has been found, surprisingly contrary to previousconsiderations, that the backscattering technique can be adapted toprecision align a patterned electron beam from a photocathode sourcewith selected areas of a major surface of a member. Moreover, theadaption as hereinafter described provides an alignment system withgreater responsiveness and in turn greater alignment accuracy thanpreviously described alignment systems, see, e.g. U.S. Pat. No.3,710,101, granted Jan. 9, 1973, U.S. Pat. application Ser. No. 370,489,filed June 15, 1973, U.S. Pat. application Ser. No. 370,558, filed June15, 1973, U.S. Pat. application Ser. No. 371,447, filed June 19, 1973,and U.S. Pat. application Ser. No. 370,115, filed June 13, 1973 all nowabandoned.

SUMMARY OF THE INVENTION A method and apparatus are provided for thealignment of a patterned electron beam projected by a photocathodesource with selected areas'of a major surface of a member with a desireddegree of accuracy such as 0.5 micron or less. The invention provides analternative alignment technique to previously described methods andapparatus and extends the application of the electron image projectionsystem in the making of precision integrated circuits.

A member such as a single-crystal silicon wafer is provided with atleast one and preferably two widely spaced apart detector marks ofpredetermined shape or shapes adjacent a major surface thereof. Eachdetector mark is capable of producing electron backscatter onirradiation by an electron beam. The predetermined shapes of thedetector marks are preferably all the same and are preferably of regulargeometric shape such as a circle, rectangle, square or triangle. Thedetector means corresponding to the detector marks are positionedadjacent periphery portions of the member, and are capable of detectingbackscattered electrons from the detector marks and producing anelectrical signal corresponding to the area of the detector markirradiated by an electron beam.

The photocathode source from which the patterned electron beam isprojected is positioned in spaced relation from the major surface of themember. The patterned electron beam to be aligned has alignment beamportions corresponding to the detector marks and of predeterminedcross-sectional shape. The photocathode source is so disposed relativeto the member that the alignment portions of the patterned electron beamirradiate the major surface close to the detector marks. The position ofthe member relative to the electron beam is varied either manually orautomatically so that the alignment portions impinge on and overlap thedetector marks. Electrical signals are thereupon produced by eachdetector means corresponding to the area of the corresponding detectormark that is irradiated by virtue of the backscattered electrons emittedby the detector marks and detected by the detector means. The electronbeam is moved relative to the member causing the electrical signalproduced by the detector means to be varied until the electrical signalindicates optimum alignment of the alignment beam portions with thecorresponding detector marks.

The alignment beam portions and the detector marks may be of anysuitable relative size within practical limits provided the shapes ofboth are predetermined. Preferably, however, each alignment beam portionis of the same cross-sectional shape as the predetermined shape of thecorresponding detector mark so that alignment can be determined simplyby reading a maximum or a minimum in the electrical signal from thedetector means. Otherwise, electrical processing of the electri-. calsignals are needed, while the alignment beam portions are oscillatedover the corresponding detector marks, to determine optimum alignment ofthe alignment beam portions with the corresponding detector marks.

The detector marks can be of any desired shape to be capable ofbackscattering electrons to the detector means. In this connection, itshould be noted that the detector marks can be defined by either anabundance of backscattered electrons or a lack of backscatteredelectrons. In either instance, the detector marks are preferably formedof a plurality of narrow, elongated angular planes which are closelyspaced in a substantially parallel arrayand which are elongatedgenerally in the direction of the corresponding detector means. It isfurther preferred that the detector marksbe formed in closely spacedpairs with the elongated angular planes of one detector marksubstantially perpendicular to the elongated angular planes of the otherdetector marks of said pair. By these preferred features, thebackscattering of electrons from the detector marks in the direction ofthe corresponding detector means is maximized and correction of thealignment beam portions to optimum alignment with the detector marks ismore rapidly and more accurately attained.

Further, it is preferred that the alignment sequence is doneautomatically by an electrical means which moves the patterned electronbeam relative to the member responsive to electrical signals from thedetector means. The electrical means preferably include for this purposea modulation means for oscillating the movement of the alignment beamportions over the corresponding detector marks; phase detection means,preferably synchronized with the modulation means, for detecting alongorthogonal axis the errors from alignment of alignment beam portions andthe corresponding detector marks, and outputting electrical signalscorresponding thereto; and actuating means for changing the electricalinput to the electromagnetic means directing the patterned electron beamfrom the photocathode source onto the major surface of the memberresponsive to the electrical signals from the phase detector means.Preferably, the electrical means also includes termination means forterminating the oscillation by the modulation means at optimum alignmentof the alignment beam portions and the corresponding detector marks.

Other details, objects and advantages of the invention will becomeapparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the sameproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, thepresent preferred embodiments of the invention and the present preferredmethods of practicing the invention are illustrated in which:

FIG. 1 is a cross-sectional view in elevation of an electron imageprojection device employing the present invention;

FIG. 2 is a fragmentary cross-sectional view in elevation taken alongline II-II of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view in perspective taken alongline III-III of FIG. 2;

FIG. 4 is a fragmentary enlarged view of a portion of thecross-sectional view shown in FIG. 2 showing the plane path ofbackscattered electrons from the detector marks to the detector means;

FIG. 5 is a graph showing the relation of backscatter emissions ofelectrons from the detector marks as shown in FIG. 4 to range of travelalong the plane in which the major surface of the member is located; and

FIG. 6 is a block diagram of an electrical circuit for the electronimage projection device shown in FIG. 1 to automatically align theelectron beam pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electron image projectiondevice suitable to practice the present invention is described in US.Pat. Nos. 3,679,497 and 3,710,101 except for the alignment technique andapparatus therefor. For convenience and clarity of description thedevice is redescribed in part here.

Referring to FIG. 1, an electron image projection device is shown. Ahermetically sealed chamber of nonmagnetic material has removable endcaps 11 and 12 to allow for disposition of apparatus into and removal ofapparatus from the chamber. A vacuum port 13 is also provided in thesidewall of chamber 10 to enable a partial vacuum to be established inthe chamber after it is hermetically sealed.

Disposed within chamber l0 is cylindrical photocathode source orelectromask 14 and alignable member 15 (e.g. a semiconductor wafer) insubstantially parallel, spaced relation. Member 15 is supported inspecimen holder 16 as more fully described later. Photocathode 14 andholder 16 are in turn positioned in substantially parallel array byannular disk-shaped supports 17 and 18, respectively. Photocathode 14and holder 16 are spaced apart with precision by tubular spacer 19 whichengages grooved flanges 20 and 21 via gaskets 22 and 23 around theperiphery of supports 17 and 18. The entire assembly is supported fromend cap 11 of chamber 10 at support 17 to allow for ease of dispositionof the photocathode source and the alignable member within the chamber.

Photocathode source 14 is made cathodic and member 15 is made anodic todirect and accelerate a patterned electron beam emitted fromphotocathode 14 to member 15. To accomplish this, holder 16 and supports17 and 18 are of highly conductive material and spacer 19 is of highlyinsulating material. A potential 19A of, for example, 10Kv, is appliedbetween supports 17 and 18. The difference in potential is conducted toand impressed on photocathode source 14 and member 15 via supports 17and 18 and holder 16.

Surrounding chamber 10 are three series of electromagnetic coils,positioned perpendicular to each other, to control the impingement ofthe patterned electron beam on member 15. Cylindrical electromagnets24,, 24 and 24 are positioned axially along the path of the electronbeam from photocathode 14 to member 15 to cause electrons to spiral andmove radially as they travel the distance from the photocathode sourceto the substrate and in turn focus the electron beam pattern. Theseelectromagnetic coils permit also control of the rotation (6) and themagnification (M) of a patterned electron beam emitted from thephotocathode source. Rectangular electromagnets 25 and 25 and 26 and 26are symmetrically positioned in Helmholtz pairs perpendicular to eachother, and to electromagnetic coils 24 -24 to cause electrons totransversely deflect as they travel the distance from the photocathodeto the member. These electromagnetic coils permit control of thedirection (in X and Y coordinates) of a patterned electron beam emittedfrom the photocathode source.

In operation, light source 27 such as a mercury vapor lamp backed byreflector 27A irradiates a photocathode layer 28 (e.g. gold orpalladium) in the photocathode source 14. The photocathode layer isirradiated through a substantially transparent substrate 29 such asquartz overlaid with a layer 30 containing the negative of a desiredcomponent pattern. The layer 30 is of material (e.g. titanium dioxide)which is opaque to the light radiation. The photocathode material isthus made electron emissive in a patterned electron beam correspondingto the desired component pattern. A part of the patterned electron beamemitted from the photocathode source 14 is preferably at least two andmost desirably four alignmentbeam portions 43 preferably of the samepredetermined cross-sectional shape (e.g. squares of 300 X 300 microns).The alignment beam portions are positioned in widely spaced away pairs,with each pair preferably positioned opposite the other pair along theperiphery of the alignment beam portions of each pair closely spaced.

Referring particularly to FIG. 2, member 15 is precision mounted withinphysically permissible limits in holder 16 and in turn with respect tophotocathode source 14. Member 15 has a flat peripheral portion 31; andholder 16 has depression 32 into which member 15 fits. Holder 16 haspins 33, 34, 35 and 36 positioned in respective quadrants around theperiphery of depression 32. Member 15 is positioned by resting flatperipheral portion 31 of member 15 against pins 33 and 34 andcurvilinear peripheral portion 37 of member 15 against pin 35. Themember is thereby located with an accuracy of about 25 microns or less.Movable pin 36, which is fitted with a compression spring 38, ispositioned and pushed against the curvilinear portion of member 15 tofirmly retain member 15 and in turn, maintain member 15 preciselylocated.

On member 15 at widely spaced apart positions preferably at oppositeperipheral portions are pairs of detector marks 39 and 40, and 41 and42. Each detector mark corresponds to an alignment beam portion 43 andhas a predetermined shape preferably the same as the predeterminedcross-sectional shape of the corresponding alignment beam portions 43.Further, each detector mark is capable of backscattering electrons onirradiation by an electron beam. Positioned adjacent the peripheryportions of member 15 at each detector mark, preferably substantially inthe plane of the major surface of the member 15 in holder 16, iscorresponding detector means 44, 45, 46 and 47, respectively. Eachdetector means, which is, for example, a scintillator-photomultipliercircuit, is capable of detecting backscattered electrons from thecorresponding detector mark and producing an electrical signalcorresponding to the area of the corresponding detector mark irradiatedby an impinging electron beam as hereinafter described.

Referring to FIG. 3, the details are shown of a preferred embodiment ofthe detector marks. Each detector mark is comprised of a plurality ofnarrow, elongated holes 48 etched in a spaced, substantially parallelarray. Each hole is typically about 1.0 micron in width, and the holesare spaced 3.0 microns apart to form in effect a grating of a largenumber of lines, e.g. 75. The width of the holes and the spacing betweenholes is, however, adjusted to the desired resolution of alignment.Additionally, each hole 48 has an elongated angular plane (i.e.curvilinear surface) 48A extending the length of the detector mark inthe general direction of the corresponding detector means, and beingvery narrow, e.g. 0.5 micron in width. Said angular plane 48A is capableof backscattering electrons to the corresponding detector means, asshown in FIGS. 2 and 4, with the effect of the electric and magneticfields present between the photocathode l4 and the member 15. Theangular planes 48A induce the electrons to preferentially emit from thedetector marks at a relatively low trajectory (e.g. to the axis ofincidence) producing large linear ranges over the plane of the majorsurface of the member under the influence of the electric and magneticfields.

Referring to FIG. 4, the relation of linear range of backscatteredelectrons as a function of the initial trajectory angle is shown.Electrons are backscattered at angles of 40, 50 and 75 to the axis ofincidence which in this embodiment is presumed to be perpendicular tothe major surface of the member. As shown, the range is not directlyproportional to the trajectory angle. The 75 and 40 trajectory 1O Kevelectrons traveled 6.4 and 4.2 millimeters, respectively, while the 50trajectory 2.5 Kev electrons traveled only 3 millimeters along the planeof the major surface.

The reason for this seemingly erratic behavior can best be explained byreference to FIG. 5. FIG. 5 shows the distribution range of Kevbackscattered electrons as a function of the initial angle oftrajectory. As seen, there are maximums at 40 and 75 and minimums at 60and 90. This distrubution curve is caused by the fact that the electronsbackscattered at 60 com- .plete approximately one full orbit in theelectric and magnetic fields before they again return to the plane ofthe major surface, while electrons backscattered at 75 and 40 completeabout onehalf and one and one-half orbits, respectively, before theyreturn to the plane of the major surface. Electrons backscattered at 90,of course, have zero range as they do not leave the plane of the majorsurface. Thus, the maximum range of 6.4 mm is achieved at a trajectoryof 75 and a secondary maximum range of 4.2 mm is achieved at atrajectory of 40 to the incidental axis.

Similarly, electrons backscattered with 2.5 Kev energy have a singlemaximum range of 3 millimeters at a trajectory angle of 50 to the axisof incidence.

The ranges above show the operability of the present invention. Furtheranalysis shows that a detector means extending from 1.5 mm to 6.5 mmfrom the backscattering point on the detector mark will collect aboutone-half of the electrons backscattered with greater than 2.0 Kev energyfrom a surface inclined at 48 to the axis of incidence of theirradiating electrons.

Further it should be observed that, although the efficiency of detectionis lower, the present invention is more sensitive then previouslydescribed alignment systems and thus provides a more accurate alignmentsystem. The lack of efficiency results from the small percentage of thesurface of the detector mark being inclined at the correct angular'plane(s) or curvilinear surfaces 48A and the small percentage ofbackscattered electrons above the threshold energy to reach the detectormeans. For example, assuming a detector mark of 0.3 mm X 0.3 mm having75 lines or holes, each hole of which contributes an angular plane atapproximately 45 of about 0.5 micron in width, only approximately lOpercent of the surface is properly inclined to backscatter detectibleelectrons. The yield of detectible backscattered electrons is furtherreduced by the fact that only about 5 percent of the backscatteredelectrons of a 10 Kev electron beam are above 2.5 Kev. Yet the presentalignment system is more sensitive because of the availability of highquality backscatter electron detectors which more than compensate forthe reduction in efficiency.

Further, it should be noted that the alignment beam portions may also bemade-up of narrow, elongated portions in a spaced, substantiallyparallel array. This embodiment is caused by the desire, in makingmatched sets of photocathode sources or electromasks and members, thatthe alignment beam portions be used to irradiate electroresist layers inthe fabrication of the detector marks for said sets. The elongatedportions of the alignment beam portions thus are the same in dimensionsto the holes 48 of the detector marks.

This embodiment is very practical in fabrication. However, it causes theelectrical signal produced by the detector means to contain highfrequency modulation superimposed on the low frequency signalcorresponding to the area of the detector mark irradiated. Thus, theelectrical signal must be processed through a highfrequency detector toobtain a low frequency AC signal corresponding to the oscillations inthe areas of the detector marks irradiated by the correspondingalignment beam portions.

in operation, the alignment beam portions 43 of predeterminedcross-section impinge on and overlap the corresponding detector marks39, 40, 41 and 42, respectively. The electron beams induce the emissionof backscattered electrons corresponding to the area of overlap betweenthe electron beams 43 and their corresponding detector marks. Alignmentcan, therefore, be accurately made simply by observing the maximumcurrent reading from electrical signals from the detector means 44, 45,46 and 47, respectively, as the electron beam from photocathode source14 is moved relative to member 115.

Where the predetermined cross-sectional shape of the alignment beamportion is different from the predetermined shape of the correspondingdetector mark, the reading of electrical signal from the correspondingdetector means to determine optimum alignment is somewhat different thanabove described. Optimum alignment is no longer indicated by the maximumor minimum in the signal readings from the detector means. Rather, aplateau is reached in the signal reading, and optimum alignment isachieved by either selecting the mean point on the plateau taking intoconsideration any differences in the geometric shapes of the alignmentbeam portions and detector marks, or selecting the mean point on thesignal rise from the detector means as the alignment beam portions moveinto or out of the areas of the corresponding detector marks. The latteralignment sequence permits alignment with the edge of the detector mark.Any of these embodiments may be readily used in either a manual orautomatic alignment system with electrical signal processing apparatussuch as that hereinafter described.

Further, manual aligning of the electron beam pattern with selectedareas of the major surface of the member may be employed irrespective ofthe embodiment of the detector marks utilized. Manual operation is,however, not preferred in commercial applications because it is timeconsuming and subject to human errors in observing the current readingin the electrical signals from the detector means. For these reasons, itis preferred that the electrical signals from the detector means beelectronically processed to control and operate alignment means such asthe electromagnetic coils 24 24 24 25 25 26, and 26 and automaticallyposition the alignment beam portions where the electrical signalsindicate optimum alignment of the alignment beam portions and thedetector marks. Not only can the optimum response position be obtainedmore rapidly, but the human error is eliminated with the same responsepoint indicated each time alignment is performed.

Referring to FIG. 10, a block diagram of electrical means is shown toautomatically align alignment beam portions 43 with detector marks 39,40, 41 and 42 and in turn precision align the patterned electron beamfrom photocathode source 14 with selected areas of the major surface ofthe member 15. The electircal signal from detector means 44 is conveyedvia lead to preamplifier 51, which amplified signal is then conveyed vialead 52 to high-frequency detector 53. In detector 53 the high frequencymodulation, caused by the elongated portions or lines of the alignmentbeam portion, is removed from the signal so that only the low frequencysignal corresponding to the area of detector mark 39 irradiated isoutputted. The output from highfrequency detector 53 passes by lead 54to tuned amplifier 55. The output of amplifier 55 passes through lead 56to a phase adjustor 57 and then through lead 58 to a phase detector 59.A gated oscillator 60 impresses a reference signal through conductors 61and 62 on the phase detector 59. The output of phase detector 56 thuscomprise the X-error signal which passes via lead 63, gate 64 and lead65 to integrator 66. The

integrator 66 has a direct-current output to adder 67,

where the output is superimposed on the alternating current,corresponding to the reference signal, from the oscillator 60 via lead68. The alternating current provides the X-component of the primaryoscillation of the alignment beam portions over the detector marks. Theadded actuating signal is passed to power and control theelectromagnetic coils 25 25,, 26 and 26 Similarly, the electrical signalfrom detector means 45 is conveyed via lead 69 to preamplifier 70, whichamplifies the signal and the amplified signal is conveyed via lead 71 tohigh-frequency detector 72. In detector 72 the high frequency modulationis removed from the signal so that only the low frequency signal isoutputted that corresponds to the varying area of detector mark 40irradiated by the corresponding alignment beam portion 43. The outputfrom highfrequency detector 72 passes by lead 73 to tuned amplifier 74.The output of amplifier 74 passes through lead 75 to phase adjustor 76and then through lead 77 to phase detector 78. Oscillator 60 impresses areference signal, which is at 90 phase angle to the signal to phasedetector 59, through conductors 79 and 80 on phase detector 78. Theoutput of phase detector 78 thus comprises the Y-error signal whichpasses via lead 79, gate 80 and lead 81 to integrator 82. Integrator 82has a direct-current output to adder 83, where the output issuperimposed on the alternating current from oscillator 60 via lead 84.The alternating current provides a the Y-component of the primaryoscillation of the alignment beam portions over the detector marks bypowering the electromagnetic coils 25,, 25 26, and 26 Similarly, thesignal from detector means 46 is conducted via lead 85 to preamplifier86, and passed thereafter via lead 87 to high frequency detector 88. Indetector 88, the high frequency modulation is removed from the signal sothat only the low frequency signal, which corresponds to the oscillationin the areas of detector mark 41 irradiated, is outputted from thedetector 88. The output from detector 88 passes via lead 89 to tunedamplifier 90 and then via lead 91 through phase adjustor 92 and lead 93to phase detector 94. Os-

cillator 60 impresses a reference signal through lead 95 on phasedetector 94. The output from phase detector 94 through lead 96 thuscorresponds to a error signal, passes through gate 97 and lead 98 tocontrol a motordriven precision potentiometer 99 to efi'ect therotational control of the electron beam pattern by increasing ordecreasing the current to the electromagnetic coils 24,, 24 and 24 Thesignal from detector means 47 is conducted via lead 100 to preamplifier101 and passes thereafter via lead 102 to high frequency detector 103.In detector 103, the high frequency modulation caused by the movement ofthe elongated portions of the corresponding alignment beam portions overdetector mark 42 is removed from the signal so that only the lowfrequency signal, which corresponds to the oscillation in the area ofdetector mark 42 irradiated, is outputted from the detector 103. Theoutput from detector 103 passes via lead 104 to tuned amplifier 105 andthence via lead 106 through phase adjustor 107 and lead 108 to phasedetector 109. Oscillator 60 impresses a signal, at 90 phase angle to thesignal to phase detector 94, through lead 1 10 to phase detector 109.The output from phase detector 109 through lead 111 in turn correspondsto a magnification (M) error signal, which passes through gate 112 andlead 113 to control a motor-driven precision potentiometer 114. Saidoutput signal controls the size of the patterned electron beam through amotor driven gang potentiometer 114 which adjusts the main focus field.

The error signals in conductors 63, 79, 96 and 111 are cross-fedelectronically via leads 115, 1 l6, 1 17 and 118, respectively, into afour input delayed null detector 119 whose output is conveyed by lead120 to a setreset flip-flop 121. The operation of the flip-flop isinitiated by actuation of a start sequence switch, whereupon currentbegins to flow via leads 122 and 123 to energize the ultraviolet source27 to cause a patterned electron beam to be emitted from photocathodesource 14, including the four alignment beam portions 43. Likewise,current from 122 passes through lead 124 to the gated oscillator 60,which in turn feeds sinusoidal signals in quadrature through leads 68and 84 to the X and Y controls 67 and 83, respectively. The entireelectron beam pattern, including the alignment beam portions 43, arethus caused to oscillate in a circle of, for example, 6 microns diameterat a frequency of 45 Hertz.

Once the aligning electron beam portions 43 are aligned on detectormarks 39, 40, 41 and 42, respectively, by operation of integrators 66and 82, and potentiometers 99 and 114, the error signals passing throughleads 115, 116, 117 and 118 reach a zero value which is detected by thenull detector 119. The null detector thereupon produces an electricalsignal which passes through lead 120 to the flip-flop 121, whichterminates the operation of the gated oscillator 60 and closes gates 64,80, 97 and 1 12 by signals through leads 125, 126, 127 and 128,respectively. The time sequence of the selective electron beam exposureof an electroresist layer on the major surface of member 15 is thenbegun and continued until the resist is fully exposed. A period of from3 to 10 seconds is usually adequate to produce a sufficient electronbeam treatment of the electroresist to cause it to be properlydifferentially soluble in selected solvents. The photocathode source 14generates a patterned electron beam from all ill the emissive areasduring the alignment period; however, the alignment period is so briefthat the electroresist on member has not been significantly exposed.

While the present invention is particularly suited and has beenspecifically described to align an electron image projection system, itis distinctly understood that the invention may be otherwise variouslyembodied and used. For example, it should be observed that, as analternative, two detector marks could be used with the automaticalignment circuit as shown in abovereferred US. Pat. No. 3,710,101. Morebroadly, the invention may be used in the procedure for precisionetching of selected areas of metal sheets to obtain desired shapes andpatterns for various scientific and industrial applications.

What is claimed is:

l. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision comprising the steps of:

A. forming adjacent a major surface of a member at least two widelyspaced apart detector marks of predetermined shape capable of producingelectron backscatter on irradiation by an electron beam;

B. positioning detector means corresponding to the detector marksadjacent periphery portions of the member;

C. detecting by the detector means backscattered electrons produced bythe detector marks and producing electrical signals corresponding to therespective areas of the detector marks irradiated by electron beams;

D. positioning a photocathode source capable of projecting an electronbeam spaced from the major surface of the member;

E. causing a patterned electron beam to be projected by the photocathodesource onto the major surface of the member, said electron beam havingalignment beam portions corresponding to the detector marks, and eachsaid alignment beam portion'having a predetermined cross-sectionalshape;

F. moving the patterned electron beam relative to the member whilecontinuing step C so that electrical signals vary; and

G. positioning the patterned electron beam relative to the member wherethe electrical signals indicate optimum alignment of the alignment beamportions with the corresponding detector marks.

2. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision as set forth in claim 1 wherein:

the detector marks are formed of narrow, elongated planes positioned inclosely spaced, substantially parallel array, said planes elongated in adirection generally toward the corresponding detector means.

3. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision as set forth in claim 2 wherein:

said detector marks are formed in widely spaced apart pairs with thedetector marks of each pair closely spaced and the narrow, elongatedplanes of the detector marks of each pair substantially perpendicular tothe narrow, elongated planes of the other detector mark of said pair ofmarks.

4. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision as set forth in claim 1 wherein:

steps F and G are automatically performed by electrically processingsaid electrical signal on oscillation of movement of the alignment beamportions over the corresponding detector marks, and steps F and G areautomatically terminated on optimum alignment of the alignment beamportions and the corresponding detector marks.

5. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision as set forth in claim 1 wherein:

each detector mark is of substantially the same predetermined shape asthe predetermined crosssectional shape of the corresponding alignmentbeam portion of the patterned electron beam.

6. Apparatus for selectively irradiating precisely located areas of themajor surface of a member comprismg:

A. a photocathode source for generating a patterned beam of electronsincluding at least one alignment beam portion of predeterminedcross-sectional shape;

B. a member positioned with a major surface thereof in spaced relationwith the photocathode source generating the patterned electron beam;

C. at least one detector mark corresponding to said alignment beamportion positioned adjacent said major surface of the member and capableof producing electron backscatter on irradiation by the patternedelectron beam, each said detector mark being of a predetermined shape;

D. means for applying a potential between the member and thephotocathode source whereby electrons from the photocathode source aredirected to and selectively irradiate portions of said major surface ofthe member;

E. electromagnetic means for directing the patterned beam of electronsfrom the photocathode source to irradiate selected portions of saidmajor surface of the member close to the selected areas, where eachalignment beam portion is directed to irradiate se lected portions ofsaid major surface close to the corresponding detector mark;

F. detector means corresponding to the detector marks positionedadjacent periphery portion of the member and capable of detectingbackscattered electrons produced by the detector mark and producingelectrical signals corresponding to the areas of the correspondingdetector marks irradiated by the alignment beam portions; and

G. electrical means for moving the patterned beam of electrons relativeto the member responsive to said electrical signals from said detectormeans to cause the alignment beam portions to substantially align withthe respective detector marks, whereby the patterned beam of electronsfrom the photocathode is located and oriented relative to the member sothat precisely located areas of the major surface of the member can beselectively irradiated with the patterned electron beam.

7. Apparatus for selectively irradiating precisely located areas of amajor surface of a substrate as set forth in claim 6 wherein:

said detector means are substantially planarly aligned with the saidmajor surface of the member.

8. Apparatus for selectively irradiating precisely located areas of amajor surface of a member as set forth in claim 6 wherein:

each detector mark is of substantially the same predetermined shape asthe predetermined crosssectional shape of a corresponding alignment beamportion.

9. Apparatus for selectively irradiating precisely located areas of amajor surface of a member as set forth in claim 6 wherein:

each detector mark comprises a plurality of narrow elongated angularplanes in a closely spaced, substantially parallel array with theangular planes elongated in a direction generally toward a detectormeans.

10. Apparatus for selectively irradiating precisely .located areas of amajor surface of a member as set forth in claim 9 wherein:

said detector marks are positioned in widely spaced pairs with thedetector marks of each pair closely spaced and the angular planes ofeach detector mark of each pair substantially perpendicular to theplanes of the other detector mark of said pair.

11. Apparatus for selectively irradiating precisely located areas of amajor surface of a member as set forth in claim 9 wherein:

each alignment beam portion of the patterned electron beam consists of"a plurality of closely spaced, substantially parallel and narrow beamportions oriented in the same direction as the angular planes of thecorresponding detector marks.

12. Apparatus for selectively irradiating precisely located areas of amajor surface of a member as set forth in claim 9 wherein:

the patterned beam of electrons generated by the photocathode sourceincludes at least two relatively widely spaced apart alignment beamportions of predetermined cross-sectional shape.

13. Apparatus for selectively irradiating precisely located areas of amajor surface of a member as set forth in claim 9 wherein:

the electrical means includes modulation means for oscillating movementof each alignment beam portion over the corresponding detector mark.phase detection means for detecting along orthogonal axis the error fromalignment of the alignment beam portions and the corresponding detectormarks and outputting an electrical signal corresponding thereto, andactuating means for changing the electrical input to the electromagneticmeans responsive to the electrical signals from the phase detector meansto bring the alignment beam portions and the detector marks intoalignment. v

1. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision comprising the steps of: A. formingadjacent a major surface of a member at least two widely spaced apartdetector marks of predetermined shape capable of producing electronbackscatter on irradiation by an electron beam; B. positioning detectormeans corresponding to the detector marks adjacent periphery portions ofthe member; C. detecting by the detector means backscattered electronsproduced by the detector marks and producing electrical signalscorresponding to the respective areas of the detector marks irradiatedby electron beams; D. positioning a photocathode source capable ofprojecting an electron beam spaced from the major surface of the member;E. causing a patterned electron beam to be projected by the photocathodesource onto the major surface of the member, said electron beam havingalignment beam portions corresponding to the detector marks, and eachsaid alignment beam portion having a predetermined cross-sectionalshape; F. moving the patterned electron beam relative to the memberwhile continuing step C so that electrical signals vary; and G.positioning the patterned electron beam relative to the member where theelectrical signals indicate optimum alignment of the alignment beamportions with the corresponding detector marks.
 2. A method of aligninga patterned electron beam generated by a photocathode source withselected areas of a major surface of a member with a high degree ofprecision as set forth in claim 1 wherein: the detector marks are formedof narrow, elongated planes positioned in closely spaced, substantiallyparallel array, said planes elongated in a direction generally towardthe corresponding detector means.
 3. A method of aligning a patternedelectron beam generated by a photocathode source with selected areas ofa major surface of a member with a high degree of precision as set forthin claim 2 wherein: said detector marks are formed in widely spacedapart pairs with the detector marks of each pair closely spaced and thenarrow, elongated planes of the detector marks of each pairsubstantially perpendicular to the narrow, elongated planes of the otherdetector mark of said pair of marks.
 4. A method of aligning a patternedelectron beam generated by a photocathode source with selected areas ofa major surface of a member with a high degree of precision as set forthin claim 1 wherein: steps F and G are automatically performed byelEctrically processing said electrical signal on oscillation ofmovement of the alignment beam portions over the corresponding detectormarks, and steps F and G are automatically terminated on optimumalignment of the alignment beam portions and the corresponding detectormarks.
 5. A method of aligning a patterned electron beam generated by aphotocathode source with selected areas of a major surface of a memberwith a high degree of precision as set forth in claim 1 wherein: eachdetector mark is of substantially the same predetermined shape as thepredetermined cross-sectional shape of the corresponding alignment beamportion of the patterned electron beam.
 6. Apparatus for selectivelyirradiating precisely located areas of the major surface of a membercomprising: A. a photocathode source for generating a patterned beam ofelectrons including at least one alignment beam portion of predeterminedcross-sectional shape; B. a member positioned with a major surfacethereof in spaced relation with the photocathode source generating thepatterned electron beam; C. at least one detector mark corresponding tosaid alignment beam portion positioned adjacent said major surface ofthe member and capable of producing electron backscatter on irradiationby the patterned electron beam, each said detector mark being of apredetermined shape; D. means for applying a potential between themember and the photocathode source whereby electrons from thephotocathode source are directed to and selectively irradiate portionsof said major surface of the member; E. electromagnetic means fordirecting the patterned beam of electrons from the photocathode sourceto irradiate selected portions of said major surface of the member closeto the selected areas, where each alignment beam portion is directed toirradiate selected portions of said major surface close to thecorresponding detector mark; F. detector means corresponding to thedetector marks positioned adjacent periphery portion of the member andcapable of detecting backscattered electrons produced by the detectormark and producing electrical signals corresponding to the areas of thecorresponding detector marks irradiated by the alignment beam portions;and G. electrical means for moving the patterned beam of electronsrelative to the member responsive to said electrical signals from saiddetector means to cause the alignment beam portions to substantiallyalign with the respective detector marks, whereby the patterned beam ofelectrons from the photocathode is located and oriented relative to themember so that precisely located areas of the major surface of themember can be selectively irradiated with the patterned electron beam.7. Apparatus for selectively irradiating precisely located areas of amajor surface of a substrate as set forth in claim 6 wherein: saiddetector means are substantially planarly aligned with the said majorsurface of the member.
 8. Apparatus for selectively irradiatingprecisely located areas of a major surface of a member as set forth inclaim 6 wherein: each detector mark is of substantially the samepredetermined shape as the predetermined cross-sectional shape of acorresponding alignment beam portion.
 9. Apparatus for selectivelyirradiating precisely located areas of a major surface of a member asset forth in claim 6 wherein: each detector mark comprises a pluralityof narrow elongated angular planes in a closely spaced, substantiallyparallel array with the angular planes elongated in a directiongenerally toward a detector means.
 10. Apparatus for selectivelyirradiating precisely located areas of a major surface of a member asset forth in claim 9 wherein: said detector marks are positioned inwidely spaced pairs with the detector marks of each pair closely spacedand the angular planes of each detector mark of each pair substantiallyperpendicular to the planes of the other detector mark of said pair. 11.Apparatus for selectively irradiating precisely located areas of a majorsurface of a member as set forth in claim 9 wherein: each alignment beamportion of the patterned electron beam consists of a plurality ofclosely spaced, substantially parallel and narrow beam portions orientedin the same direction as the angular planes of the correspondingdetector marks.
 12. Apparatus for selectively irradiating preciselylocated areas of a major surface of a member as set forth in claim 9wherein: the patterned beam of electrons generated by the photocathodesource includes at least two relatively widely spaced apart alignmentbeam portions of predetermined cross-sectional shape.
 13. Apparatus forselectively irradiating precisely located areas of a major surface of amember as set forth in claim 9 wherein: the electrical means includesmodulation means for oscillating movement of each alignment beam portionover the corresponding detector mark, phase detection means fordetecting along orthogonal axis the error from alignment of thealignment beam portions and the corresponding detector marks andoutputting an electrical signal corresponding thereto, and actuatingmeans for changing the electrical input to the electromagnetic meansresponsive to the electrical signals from the phase detector means tobring the alignment beam portions and the detector marks into alignment.